Semantics-Directed Prototyping of Hardware Runtime Monitors

Building memory protection mechanisms into embedded hardware is attractive because it has the potential to neutralize a host of software-based attacks with relatively small performance overhead. A hardware monitor, being at the lowest level of the system stack, is more difficult to bypass than a software monitor and hardware-based protections are also potentially more fine-grained than is possible in software: an individual instruction executing on a processor may entail multiple memory accesses, all of which may be tracked in hardware. Finally, hardware-based protection can be performed without the necessity of altering application binaries. This article presents a proof-of-concept codesign of a small embedded processor with a hardware monitor protecting against ROP-style code reuse attacks. While the case study is small, it indicates, we argue, an approach to rapid-prototyping runtime monitors in hardware that is quick, flexible, and extensible as well as being amenable to formal verification.